We will study the signals received by resting B cells which cause their activation, proliferation and differentiation to the state of antibody synthesis and secretion. We will focus primarily on the role of T cells and macrophages in this process. Specifically we will identify the non-specific activities in the supernatants of Concanavalin A stimulated spleen cells which drive the latter stages of the B cell response. In addition we will study the antigen-specific T cell activity involved in the initial state of the B cell response to soluble but not red blood cell bound antigens. In this effort we will rely heavily on the production of T cell hybridomas as sources of high titered pure, T cell activities.